This project will focus mainly on the function of neuropeptides in the visual system and the relationships and interactions between neuropeptides and other neurotransmitter systems. The first step of the study is to figure out which peptides, such as substance P, enkephalins, somatostatin and LHRH are present and their content in the retina of fish, frog, chick and rabbit. This will be performed by radioimmunoassay and radioreceptor assay and these peptidergic neurons will be localized immunohistochemically. After their presence have been established, their function in the retina will be studied. If they are to be considered as neurotransmitters, demonstration of their release from nerve terminals in response to light and depolarizing stimuli is an essential prerequisite. The peptide content and the rate of peptide formed in the retina under dark and light adaption also will be studied. This study will provide the information whether they are involved in the information transmission. The relation of peptidergic neurons with other transmitter systems will be studied by (a) the effect of other putative neurotransmitters on the peptide release; (b) the effect of peptides on the release of other transmitters; and (c) using double staining techniques on the same section or different techniques on serial tissue sections. The development of peptides and their precursors in the retina will be studied by radioimmunoassay and radioreceptor assay. Consequently, the biochemically changes can be correlated with morphological development.